Spontaneous Parametric Down-conversion Process, The Measurement Of Single Photon And Quantum State Reconstruction

As a nonciassical state, the single-photon state has applications in many areas, such as in basic quantum optics research, quantum communication, quantum computation etc. Because of its quantum property, single-photon state can avoid eavesdropping and has more advantages in information security transferring than the classical state. There are many ways to generate single-photon state, e.g. attenuated laser, quantum dot, pulsed excitation of a single dipole, single nitrogen-vacancy color center in a diamond nanocrystal, cavity-QED and spontaneous parametric down-conversion (SPDC). Because SPDC creates photons in pairs, if one photon is found in one arm of the twin-photon, we know there must exists a single-photon state in another arm. So, we can assure when the single-photon state generate without detecting it. And the SPDC has also been widely studied for its entanglement of time, space, polarization, and energy.In order to get single-photon state and reconstruct its Wigner function, The two aspects, SPDC of pulse pumped nonlinear phase match type I BBO crystal and reconstruction of Wigner function of quantum state, are studied in this thesis.1. The relationship of cut-angle and the degree between pump beam and signal beam in BBO crystal pumped by 425nm pulse is theoretically calculated. 28.7° cut-angle BBO crystal is chose for our use, which correspond to a 5° angle between pump beam and signal beam.2.We measure the down-conversion ring with CCD and analysis the thickness of the down-conversion ring.3. The effect of pump beam's walk-off and the group-velocity-mismatch in BBO crystal is discussed, the group-velocity-mismatch can be compensated by non-collinear phase-match when the angle between signal and idler beams equals to 14°.4. The maximum 50500 photo counts per second with 76MHz pump pulse frequency is detected. The probability to be single-photon state of every count is better than 99%5. As a primary work for reconstructing Wigner function of single photon state, we reconstruct Wigner function of vacuum and coherent state. The effect of kc and the number of the data is discussed in the process of reconstruction.